2. Briefing about SQUIDGeneral Applications Our Application to NDT in Aluminum Plates

3.  SQUID stands for: Superconducting Quantum Interference Device  SQUID is a very sensitive Magnetic Flux detector  SQUID is Flux-To-Voltage Transducer  Output of Voltage of SQUID is periodic with Flux Quantum Period ф o =h/2e=2.07x10 -15 Web  So far, SQUID is the most sensitive device.

4. 10 -4 Field (T) SQUID 10 6 Line frequency and harmonics Frequency (Hz) fluxgate 10 -2 10 -1 10 -0 10 1 10 2 10 3 10 4 10 5 Lab noise 10 -16 10 -15 10 -14 10 -13 10 -12 10 -11 10 -10 10 -9 10 -8 10 -7 fT pT nT MR sensors MCG MEG Earth’s field

5. noise threshold

6.  In principle: SQUID can measure any thing that can provide magnetic flux:  Current  Brain Signals  Heart Signals  Magnetization  None-Destructive Testing  Geophysics  Astrophysics

7.  SQUID combines few Physical Phenomena:  Flux Quantization (in a Closed Sup. Loop)  electron-pair wave coherence  Josephson Tunneling  Two Types of SQUIDs available:  DC- SQUID (Biased using DC current)  RF- SQUID (Biased using rf current)

8. Single Channel Magnetometer Single Channel Gradiometer Multichannel Scanning System

11. Bulk RF-SQUID Gradiometer (Hand made)

12.  Applying External Mag. field to the Ring   Phase Change across the Links  1 = |  1 (x)| e i  1,  2 = |  2 | e i  2 Superconductor,  1 WeakLink Superconductor,  1

13.  Also a current i will loop around the ring  This current shall cancel the B ext  But this does not happen because of the critical current across the Link  Total Phase Change must = 2πn  Total Phase change due to applied Mag. Field:

14.  Tota Phase Change = 2πn   a phase due to current i is made to justfy the total phase change: 

15.  Current moves clockwise or (counterclockwise) the magnitude of i increases to a maximum

16.  Result is:  Circulating current is periodic with applied magnetic field. The period is Ф o

17. Visual InspectionAcoustic SoundingSurface Hardness methodUltrasonic TestingImpulse ResponseMagnetic MethodsResonant FrequencyInfrared ThermographyRadioactive Testing

18. Evaluating cracks in metals no matter how deep Evaluating Corrosion in concrete without contact Output can be contour like for more details of defect.

19. 19 Need ~1 picotesla sensitivity for real time monitoring Cardiac magnetic signal

20. Low-T c dc SQUID systems for MCG application CardioMag Imaging, Inc., USA

21. P QRS T

22. Healthy heart Abnormal Measured by a 9-channel CMI-3609 system, CardioMag Imaging, Inc. USA

23.  Non-contact  Non-invasive  No radiation  Safe  Accurate MCG ECG Nuclear scan Magnetocardiograph

24. 24 Need non-destructive test for corrosion, cracks, and stress Eddy currents imaged with scanned GMR reveal invisible corrosion. Field image Optical image “The crack was in the upper row of rivets along The S-10L lap joint…” excerpt from NTSB report

25. Scan of 1, 3, 5, and 10 mm holes in a steel plate

29. Solving Maxwell Equations for the Applied magnetic field in the Near zone only:

30. The measured field signal is described by a vector. The vector magnitude and angle represent the amplitude and phase angle of the detected signal respectively

31. In terms of the field amplitudes, the result shows that the attenuation of a magnetic dipole field through a metal is significantly less than the calculated attenuation of plane wave given by the Equation:

32. The reason of less attenuation is ascribed to the fact that usually the attenuation of the field is caused by the shielding effect of the induced current which is normally in opposite phase to the source current. However, the low frequency small circular shielding current induced by a magnetic dipole has a different phase shift. Hence, the orthogonal component of that shielding current causes no significant shielding effect. Thus, attenuation is less than that calculated for a plane magnetic wave. This better attenuation property of a dipole field inside a metal can be applied beneficially for the NDT.

34.  SQUID has been successfully used for:  Biomagnetic Applications  Non-Destructive Evaluation ( NDE)  Geophysical Applications  Scanning SQUID Microscope